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Mészáros grb-gen06
GRBin the Swift Era
and beyond
Peter MészárosPennsylvania State University
1
Mészáros Tok06
GRB: basic numbers• Rate: ~ 1/day inside a Hubble radius• Distance: 0.1 ≤ z ≤ 6.3 ! → D ~ 10 28 cm • Fluence: ~10-4 -10-7 erg/cm2
~ 1 ph/cm2 (g-rays !)• Energy output: 1053 (Ω/4π) D2
28.5 F-5 erg but, jet: (Ωj/4π) ~ 10-2 → E γ,tot ~ 1051 erg
→ E γ,tot ~ LΘ x 1010 year ~ Lgal x 1 year• Rate[GRB (γ-obs)] ~10-6(2π/ Ω) /yr/gal →1/day (z ≤ 3) but Rate [GRB (uncollimated)] ~ 10-4 /yr/gal, while Rate [SN (core collapse] ~ 1O-2/yr/gal, or 107 /yr ~ 1/s (z <3)
Mészáros grb-gen06
3
Mészáros grb-gen06
`
←↓Short (tg< 2 s)
→↑Long (tg >2 s)
GRB: standard paradigm Bimodal distribution of tγ duration
3d group? ↓
Mészáros, L’Aqu05
BH + accr. Torus Jet
• Both collapsar or merger → BH+accr.torus→fireball
• Massive rot. *: sideways pressure confines/channel outflow → fireball Jet
• Nuclear density hot torus → can have nn→e± jet
• Hot infall →convective dynamo → B~1015 G, twisted
(thread BH?) →Alfvénic or e±pγ jet• (Note: magnetar might do similar)
Mészáros, L’Aqu05
Explosion FIREBALL
• E γ ~ 1051 Ω-2 D2
28.5 F-5 erg • R0 ~ c t0 ~ 107 t-3 cm Huge energy in very small volume • τγγ ~ (Eγ/R3
0mec2)σTR0 >> 1 → Fireball: e±,γ,p relativistic gas• Lγ~Eγ/t0 >> LEdd → expanding (v~c) fireball (Cavallo & Rees, 1978 MN 183:359)
• Observe Eγ> 10 GeV …but γγ→e±, degrade 10 GeV →0.5 MeV? Eγ Et >2(mec2)2/(1-cosΘ)~4(mec2)2/Θ2
Ultrarelativistic flow → Γ ≥ Θ-1 ~ 102
(Fenimore etal 93; Baring & Harding 94)
Mészáros grb-gen06
Relativistic Outflows• Energy-impulse tensor : Tik = w ui uk + p gik , ui : 4-velocity, gik= metric, g11=g22=g33=-g00=1, others 0; ultra-rel. enthalpy: w = 4p ∝ n4/3 ; w, p, n : in comoving-frame • 1-D motion : ui=(γ,u,0,0), where u = Γ (v/c), v = 3-velocity, A= outflow channel cross section : • Impulse flux Q=(w u2 +p) A energy flux L= wu Γ c A particle number flux J= n u A• Isentropic flow : L, J constant → w Γ /n = constant (relativistic Bernoulli equation); for ultra-rel. equ. of state p ∝ w ∝ n4/3 , and cross section A ∝ r2 → n ∝ 1 / r2 Γ comoving density drops → Γ ∝ r “bulk” Lorentz factor initially grows with r.
• But, eventually saturates, Γ→Ej/Mjc2 ~ constant
Γ
r
Mészáros grb-gen06
Shock formation• Collisionless shocks (rarefied gas)• “Internal” shock waves: where ? If two gas shells ejected with Δ Γ = Γ1-Γ2~ Γ, starting at time
intervals Δt ~tv ,, they collide at ris ,
ris ~ 2 c Δt Γ 2 ~ 2 c tv Γ 2 ~ 1O12 t-3 Γ 22 cm (internal shock) [Alternative picture: magnetic dissipation, reconnection]
• “External shock”: merged ejected shells coast out to res, where they have swept up enough enough external matter to slow down, E=(4p/3)res
3 next mp c2 Γ 2,
res~ (3E/4pnextmpc2)1/3 Γ-2/3 ~ 3.1O16(E51/nO)1/3 Γ2-2/3 cm
(external shock)
Mészáros grb-glast06
XO
R
Internal Shock
Fireball Model: long GRBs
External Shock
Collisions betw. diff. parts of the flow
The Flow decelerating into the surrounding medium
GRB Afterglow
E.g., recent review on GRB-Swift results & implications: Mészáros, 2006, Rev.Prog.Phys 69:2259 (astro-ph/0605208 )
Mészáros grb-gen06
Internal & External Shocksin optically thin medium :
LONG-TERM BEHAVIOR
• Internal shocks (or other, e.g. magnetic dissipation) at radius ri~1012cm
→γ-rays (burst, tγ ~sec)
• External shocks at re ~1016cm; progressively decelerate, get
weaker and redder in time (Rees & Meszaros 92)
• Decreasing Doppler boost: → roughly, expect radio @ ~1 week , optical @ ~1 day (Paczynski, & Rhoads 93, Katz 94)
• PREDICTION : Full quantitative theory of:• External forward shock spectrum softens in time: X-ray, optical, radio … →long fading afterglow (t ~ min, hr, day, month)• External reverse shock (less
relativistic, cooler, denser): Prompt Optical → quick fading ( t ~ mins) (Meszaros & Rees 1997 ApJ 476,232)
Γ
rrc ri re
Int
Ext
Rø
Mészáros grb-gen06
Standard External Forw. & Rev. Shock Synchroton & IC spectrum
Lower energy:Synchrotron(reverse: eV, forward: MeV)
Higher energy:Inv. Compton (forward: GeV)
R:sy
F:sy
F:IC
Mészáros grb-gen06
Shock Photon Spectrum• Non-thermal power law
spectrum, both in int. and ext. shocks, due to
• Synchrotron, peak at ~200 keV (or ~ eV?)
• Inv. Compton, peak ~ GeV (or ~200 keV ?
• Sy peak location, ratio Sy/IC dep. on Bsh , γe, Γ
• Peak softens with time• Ratio Sy/IC decr w. time
E
E2NE
Sy
IC
t
tF
E
E
X,OR g
Mészáros, L’Aqu05
GRB 970228 : BeppoSAX Discovery of an afterglow
• X-ray location:2-3 arcmin → raster
• →optical (arcsec) & radio location
• Can identify host galaxy, redshift
• located at cosmological dist. NEW ERA!Feb 28 March 3
F_x ~3E-12 erg.cm2/keV/s , decr. By 1/20
(Costa et al 1997, Nature 387:783)
Mészáros, L’Aqu05
GRB afterglow blast wave model
• Simplest case: adiabatic forward shock synchrotron rad’n from shock-accel. non-thermal e-
• F(ν,t) ∝ ν-β t -α • α = (3/2) β • Parameters E0, εe, εB,
(β=(p-1)/2)GRB 970228 as blast wave: Wijers, Rees & Mészárosl 97 MNRAS 288:L51 fit to
Mészáros, Rees 97 ApJ 476:232 model
Mészáros, L’Aqu05
Snapshot Afterglow Fits
• Simplest case: tcool(γm)>texp, where N(γ)∝γ-p for
γ>γm (i.e. γc(ool) >γm) • 3 breaks: νa(bs), νm, νc
• Fν ∝ ν2 (ν5/2) ; ν<νa ; ∝ν1/3 ; νa<ν<νm ; ∝ν-(p-1)/2 ; νm<ν<νc ∝ν-p/2 ; ν>νc
(Mészáros, Rees & Wijers ’98 ApJ 499:301)
Sari, Piran, Narayan ’98 ApJ(Let) 497:L17)
Break frequency decreases in time (at rate dep. on whether ext medium homog. or wind (e.g. n∝r-2 )
Mészáros, L’Aqu05
Collapsar & SN : a direct link - but always ?
• Core collapse of star w. Mt~30 Msun
→ BH + disk (if fast rot.core) → jet (MHD? baryonic? high Γ, + SNR envelope eject (?)• 3D hydro simulations (Newtonian SR) show that baryonic jet w. high G can be formed/escape• SNR: not seen numerically yet (but: several suggestive observations, e.g. late l.c. hump + reddening; and ..• Direct observational (spectroscopic)
detections of GRB/ccSN
Collapsar & SN ANIMATION
Credit: Derek Fox & NASA
Mészáros, L’Aqu05
GRB 030329 - SN 2003dh & others• 2nd Nearest “unequivocal”
cosmological GRB: z=0.17• GRB-SN association: “strong”• Fluence:10-4 erg cm-2 , among highest in BATSE, but tγ~30s, nearby; Eg,iso~1050.5erg:
~typical,• ESN2003dh,iso ~1052.3 erg ~ ESN1998bw,iso («grb980425) vsn,ej ~0.1c (→ “hypernova”)• GRB-SN simultaneous? at most: < 2 days off-set (from opt. lightcurve)
( → i.e. not a “supra-nova”)• But: might be 2-stage (<2 day delay) *- NS-BH collapse ? → ν predictions may test this !
• Some others: GRB 031203/SN2003lw;
- GRB 060218/SN2006aj; ...
Collapsar & ccSN :
Mészáros, L’Aqu05
Light curve break: Jet Edge Effects
• Monochromatic break in light curve time power law behavior
• expect Γ∝t-3/8, as long as ϑlight cone
~Γ-1 < ϑjet, (spherical approx is valid)
• “see” jet edge at Γ ~ ϑjet-1
• Before edge, F ν∝(r/Γ)2.Iν • After edge, Fν∝ (r ϑjet)2.Iν ,
→ Fν steeper by Γ2∝t-3/4
• After edge, also side exp. → further steepen Fν ∝t-p
Mészáros, L’Aqu05
GRB 030329:• evidence for
SN • evidence for refreshed shock and • evidence for 2-comp. jet: ϑγ ~5o
< ϑradio ~17o
Berger etal 03, Nature 426, 154
More recently (Swift): several XR light-curve breaks, but: conflicting evidence for (a?)chromatic breaks
Mészáros, L’Aqu05
Jet Collimation& Energetics
• ↑Jet opening angle inv. corr. w. Lγ (iso)
• ← Lγ(corr) ~ const.
• Mean collim. “correction” <(4π/2ΔΩj)> ~ 10-2
• GRB030329: 2-comp. jet? ϑg~5o < ϑradio ~17o
• → Etotal = Eγ+Ekin ~ const.
( → quasi-standard candle )
Berger etal 03
Frail et al 01
Mészáros, L’Aqu05
Epk vs Eγtot Better correl. than Epk vs Eγiso (?)Ghirlanda, Ghisellini, Lazatti, aph/0405602 (see also Friedman & Bloom, aph/0408413) Epk ∝ Eγ0.7
Mészáros, L’Aqu05
z-measures?
• Variability V vs. Eγ, iso (Fenimore, Ramirez-Ruiz, Reichart..)
• Lag vs. Eγiso (Norris, Bonnell,..)
• Hardness (Epk) vs. Eγ,iso (Amati etal, Bagoly etal, Schmidt..)
• Epk vs. Eγ ,jet (Ghirlanda et al 04) • Epk vs. Eiso vs. tbreak (Liang & Zhang 05)
• Epk vs Eiso vs. t0.45 (Firmani et al, 06; where t0.45 ~ V)
Mészáros, L’Aqu05
Reasons for Amati - Ghirlanda?• E.g, internal shocks, Ep ~ Esy ~ ΓB'γe
2 ~ΓB' ~ B ~ U1/2
~ (L/r2) 1/2 ~ L1/2 tv-1 Γ-2 (Zhang, Mészáros 02 ApJ 581, 1236)
( since r~ ctv Γ2 - but, is tv , Γ ~ const. for diff. L? )• E.g photospheric characteristic temperature, Ep ~ Γ T’ ~ Γ (L/Γ2 rph
2)1/4 ~ Γ2L-1/4 (since rph ~ L/Γ3 ) ; if use Frail : L ~ θ-2 , and causality : Γ~ θ-1
→ Ep ~ L 3/4 (Rees, Mészáros 05 ApJ 628, 847)
• If photosphere is at known radius of WR *, Ep ~ Γ T’ ~ Γ (L/Γ2 R*
2)1/4 ~ Γ1/2 L1/4 ; bulk of fluid moves at Γ~3-1/2 θ-1 since outside that KH mix → Ep ~ L 1/2 (Thompson astroph/0507387;
Thompson, Meszaros & Rees, aph/0608....)
Mészáros, L’Aqu05
9mag! (z=1.6)
GRB
Optical Flash : GRB 990123
ROTSE
(Akerlof et al. 1999; Meszaros & Rees 1997; Sari & Piran 1999; Kobayashi 2000)
Mészáros, L’Aqu05
Prompt Optical Flashes
• GRB 990123 → bright (9th mag) prompt opt. transient (Akerlof etal 99)
– 1st 10 min: decay steeper than forw. shock • Interpreted as reverse external shock
(pred : Mészáros&Rees ’97) • 99-02: Great Desert: Lack of flashes, upper limits mv~12-15
• but: New generation robotic tels: ROTSE III, Super-LOTIS, RAPTOR, KAIT, TAROT, NEAT, Faulkes, REM; etc
• → more prompt optical flashes, e.g. : GRB 021004, 021211 ; and new “semi- prompt” flashes : GRB 030418, 30723 : ≠ GRB 990123 ! → t >211, 50 s resp, see forw. shock only? • and now... Swift era: GRB 041219A (Raptor; Vestrand 05); GRB 050319 (Raptor; Wozniak et al 05) GRB 050401 (Rotse III, Quimby et al, 05) GRB 050801 (Rotse III, Rykoff et al 05) GRB 050904 (TAROT, Gendre et al, 06) GRB 060206 (Raptor, Wozniak et al, 06)
Akerlof etal ’99
Kulkarni et al ’99
nFn
n
Sy (rev)
Sy (forw)
0 X,g
Mészáros, L’Aqu05
Cosmology with GRBs?High-z GRB distance measures
Lamb, Reichart 00
•Positive K-correction: → flux ~ constant at z ≳ 3•Optical/UV: Ly α cutoff → redshift out to z<5 for Swift•Forward shock exp. fluxes¯
O/IR Ciardi & Loeb 00
Mészáros, L’Aqu05
IR & XR hi-z detectabilityXR detectability ¯
V-band
K-band
JWST
ROTSE
O/IR zx detectability
Chandra
Swift
Gou et al, 03, ApJ 604:508
Mészáros, L’Aqu05
BAT: Energy Range: 15-150kevFoV: 2.0 srBurst Detection Rate: 100 bursts/yr
UVOT: Wavelength Range: 170-650nm
Three instrumentsGamma-ray, X-ray and optical/UV
Slew time: 20-70 s !
XRT: Energy Range: 0.2-10 keV
SWIFT
Launched Nov 04
>95% of triggers yield XRT det>50% triggers yield UVOT det.
Mészáros grb-gen06
SWIFT: New Results
• > 140 new afterglows localized since launch• Redshifts for >40 long GRB and 4 short GRB• <zlong> ~2.4-2.8, which is 2x Beppo-Sax distance (i.e. significantly fainter & redder, than Beppo-Sax afterglows!)• <zshort> ~0.1-0.7; Lshort~ 10-2 Llong ; compact merger• XR light curves (102s-104s): new features (both long and short) - steep + shallow decay, flares → evidence for continued activity?
In the period 1 min < t < hrs,new features show up, which may be natural extensions of thestandard burst & AG model (or ..?)
Mészáros grb-gen06
SWIFT: New Results, cont.
• Short bursts localized, hosts identified, redshifts measured
• VHZ (very high redshift) bursts: several >5, one 6.29
• Prompt optical/IR flashes (one very bright)• GRB/SN, at least two spectroscopic, more ...
Mészáros grb-gen06
New features seen by Swift :A Generic X-ray Lightcurve
~ -3
~ -0.5
~ - 1.3
~ -2102 – 103 s 104 – 105 s
105 – 106 s
( 1 min ≤ t ≤ hours )
oldnew
BUT: not all features in all bursts
Mészáros grb-gen06
Afterglow: when does it start?
• standard interpretation: AG starts at tdec ~ (3/4) (rdec/2 c Γ2 ) (1+z) ~ (3/8 c Γ2)(3E/4π n mp c2 Γ2)1/3 (1+z) ~ 102 (E52/n0)1/3 Γ2
-8/3 (1+z) s
• But, for prompt duration T=Tγ =Toutflow ~ T90 - “Thin shell”: T < tdec → AG start at tdec above - “Thick shell”: T > tdec → AG start at T~Tγ~T90
Mészáros grb-gen06
Example : GRB 050315
0
12
34
Vaughn et al. 2005
t -0.4t -0.7
ν -0.73±0.11
t -5.2
ν -1.9±0.9
Mészáros grb-gen06
Initial steep drop:Fx ∝ (t-t0 )-α
• Current bet: tail end of GRB (high latitude emission) :
radiation from outside main beam, θ>Γ-1
- arrives at t ~ Rθ2/2c later than from θ~0, - is softer by D~t-1 (Nousek et al 05, Zhang et al 05, Panaitescu et al 05))
• expect α=2+β , where F~ tανβ (Kumar, Panaitescu 00)
~ OK , generally; departures may be understood• Possible alternatives: - Cocoon radiation escape (Pe’er, et al, ApJ 06 in press, aph/...)
- Photopion rapid cooling --> drop (Dermer, 06, aph/....)
Mészáros grb-gen06
Initial rapid decay:
High latitude emission
Radiation Components:
• 1 : Prompt γ-rays (GRB) from l.o.s. angles θ < Γ-1
• 2 : tail-end of GRB, from high latitude emission : γ-rays emited promptly, but from angles θ >Γ-1 ; arrive at time
t ~ Rθ2/2c later than from θ~0, and is softer by D~t-1; expect
α=2+β , ~ OK
• 3 : afterglow, from forward shock at l.o.s.angles θ < Γ-1 ;
later than (or partially overlap with) high latitude comp. (2)
11
2
3
Mészáros grb-gen06
High latitude issues…• Time slope α depends on choice of t0 → can fit t0 such that slope is satisfied
i.e., determine tdec ? (Liang et al astroph/0602142)
• When T > tdec (and also when T< tdec) can have an admixture of (a) afterglow (l.o.s) θ<Γ-1 , and (b) high latitude θ>Γ-1 components. Generally βprompt <βsteep , so can accommodate steeper decays than 2+ βprompt (O’Brien et al, 05)
• Flares: t0 fit can give pulse ejection time by engine (Liang et al 06)
• Structured jet: for on-beam viewing jet shape has little effect, but off-beam can get shallower slope (Dyks et al aph/0511699)
• From initial steep decay slope, t0 constraints suggest t0 ~ ttrigger, may infer prompt emission radius Rγ (Lazzati, Begelman aph/0511658)
Mészáros grb-gen06
37
Liang, et alaph/0602142
Retrofit:The t0 which fits the steep decay slope generally agrees with the onset of the rising segment of the last peak before the decay
Mészáros grb-gen06
Shallow decay
• Slope 0.3 ≤ α ≤ 1 : likely due to “refreshed shock” … I.e. the forward afterglow shock receives continued
reinforcement from late-arriving ejecta NOTE: late arriving, but not necessarily late ejected! (Rees-Meszaros 98, Panaitescu, PM, MJR 98, Kumar-Piran 00, Sari-Meszaros 00,
Nousek et al 05, Zhang et al 05, Granot-Kumar 05)
Mészáros grb-gen06
Shallow decay (0.2 ≤ α ≤ 1)
• Probably due to refreshed shocks, due either to:
• Long duration ejection (t ~ tflat ) ; or• Short duration ejection (t ~ tγ), but with range of Γ,
e.g. M(Γ)~ Γ-s , E(Γ) ~ Γ-s+1 , for ρ~r-g ext. medium :
e.g. FS: α=[-4-4s+g+sg+β(24-7g+sg)]/[2(7+s-2g)]
Rees+PM, 98 ApJ 496, L1 ; Sari +PM, 00, ApJ 535, L33 ; Zhang +PM 01, ApJ 552, L35
Slow Γ,refreshed→
Note : Fit to Swift data ⇒ Γ distrib. may be a broken power law(Granot, Kumar astro-ph/0511049)
Mészáros grb-gen06
Refreshed (shallow decay)• Note : EXshallow ≤ Eγprompt [O’Brien, et al, 06]. But in order for refreshed shock to dominate the afterglow, energy input in refreshed component needs exceed that in prompt • ⇒ either - rad’n. effic. εγ > εx (eg prompt is Poynting dominated ?..)
or - fraction of refreshed shock energy undetected (IR? GeV?…) or - preactivity evacuates cavity, or fraction of energy into electrons ∝t1/2 (Ioka et al, astro-ph/0511749
• Alternative : shallow decay due to emission from anisotropic jet lines of sight just outside sharp edge of main bright jet (Eichler-Granot astroph/0509857)
• Other possibilities:
- Ekin underestimated (also in BATSE), so εγ is reasonable relative to εx
- Two-component jet (narrow-fast/broad-slow) (Granot, et al, astroph/0601056)
Mészáros grb-gen06
Giant X-ray Flare: GRB050502b
500x increase!
GRB Fluence:8E-7 ergs/cm2
Flare Fluence:9E-7 ergs/cm2
Burrows et al. 2005, Science; Falcone et al. 2005, ApJ
Mészáros grb-gen06
XR Flares• Main puzzles: - large energy Exfl ≤ 0.1-1 Eγprompt
- steep rise/decay F∝ (t-t0)α, α~±3-6 • Possible causes: - refreshed (forward) shocks (rise & decay too shallow)
- reverse IC component (one shot affair- where is forward?)
- interaction with external matter ( rise/decay slope?)
- continued central engine activity, e.g. internal shocks, dissipation (difficult for central engine, but address temp. slope, total energy - less problematic than others ?)
Mészáros grb-gen06
XR Flare triggers?
• Gravitational instability → disk fragmentation → lumpy accretion
(Perna, Armitage, B.Zhang)
• MHD accretion- magnetic tension (“springy”) → lumpy accretion
(Proga & Begelman, Fan, Proga &B.Zhang)
• Short bursts: BH-NS disr (SPH GR numerical) → prompt accretion + extended tail → delayed lumpy accretion (Davies, et al 05; Lee et al 00, Rosswog et al 04; Laguna, Rasio 05)
Mészáros grb-gen06
MHD accretion?
(Proga & Begelman 03)
Accretion rate
time
Mészáros grb-gen06
Main Possible Explanations of long GRB afterglow new features
• Initial drop: likely due to tail end of GRB (high latitude emission) : rad’n from θ>Γ-1 arrives at t ~ Rθ2/2c later than from θ~0, is softer by D~t-1; expect α=2+β , ~ OK
• Shallow decay: probably “refreshed shocks”, either from Longer ejection (t ~ tflat ) ; or Short ejection (t ~ tγ), but with range
of Γ, e.g. M(Γ)~ Γ-s , E(Γ) ~ Γ-s+1
• Flares: likely due to continued central engine activity : main constraints: very sharp rise and decline (t±3 ←→ t±6)
• But: remains work in progress- depending also on new observations
Mészáros grb-gen06
Short & Long Afterglows
• Big question: are they the same?• 0th order answer: looks like yes - initial steep decay - XR flares - “normal forward shock” decay - jet break • But: 1st order differences are interesting - Avg. kin. energy/solid angle x100 smaller - Avg. jet angle x2 larger than in long bursts (Fox et al 05, Panaitescu 05)
Mészáros grb-gen06
Short Bursts
- Hosts: E , Irr , SFR (compat. W. NS merg, but: some SGR, other?)- Redshift : < 0.1 to ~ 0.7- XR, OT, RT: yes (mostly)- XR l.c.: similar to long bursts? (XR bumps too- late engine?)
050724 050509b
050709b
Mészáros grb-gen06
SHB afterglow fits• So far, > 11 shb afterglows, 5-6 hosts ( D. Fox talk, Nature 05)
• AG fits for 050709 (Irr), 050724 (E) (Panaitescu, aph/0511588)
Using fluxes and break times, standard ag model: Γ = 6.5 (E50/n0)1/8 td-3/8 , θj=Γ(tb)-1
→ θj = 9o (n0/E50)1/8 tbd 3/8 ,
Ej = πθj2E ~ 1049 n0
1/4 (E50 tbd)3/4 erg High /low dens. soln’s: 050709 : θj >6o , 10-4 < n < 10-1 cm-3 , E~3-300 x 1050 erg/s
θj >2o , n < 10-5 cm-3 , E~2-10 x 1049 erg/sr
050724 : θj >8o , 10-1 < n < 103 cm-3 , E~1-50 x 1049 erg/sr • but: GRB 050724 (Grupe et al, 06, in prep.) Chandra late obs.:
no break seen.• while: GRB 051221A : Swift + 2 Chandra obs. : well defined
jet break appears @ 4 days ⇒ θj ~ 7 o, Ej ~ 2. 1049 erg
Mészáros grb-gen06
Short burst paradigm:
NS-NS or NS-BH
merger
BH + accretion
• Paradigm seems compatible with hosts, and (for Kerr BH-NS) some simulations suggest extended activity & flares ⇒
simulationLaguna, Rasio 06;( Preliminary )
Mészáros grb-gen06
BH-NS merger?(Laguna & Rasio ‘06)
50Schwarz.BH-NS Kerr-proBH-NS
Mészáros grb-gen06
Prompt optical afterglows
• ⇐ expected behavior: reverse shock causes prompt (10’s of sec) bright (mV ≥ 9) optical flash, decaying much faster than long-lasting forward shock optical afterglow (Mészáros-Rees 97)
• First seen in GRB 990123 ⇐ Rotse (Akerlof et al 99), and few
other bursts, but rare : why?• Could be that - rev.shock hi-mag→suppress? - pair formation →spec. to IR ? - rev. shock rel. →spec. to UV ?• Latest : GRB 050904 (z=6.29) shows prompt bright opt flash !
Gou et al 04
R
F
γ O
O
Mészáros grb-gen06
long burst from
Swift ( z=6.29 ): GRB050904
• Discovered/localized by Swift BAT, XRT, UVOT• Prompt ground I,R band TAROT,
P60 upper limits, • Detection J=17 mag FUN/SOAR,
VLT → photometric z >6• Spectroscopy Subaru 8.5 m @ t=3.5 day : z = 6.29 !
(“usual” low z grb)
(time-dilated hi-z grb) Most distant
Mészáros grb-gen06
GRB 050904 as an XR beacon
• At a redshift z=6.29 (~reionization; most distant
known known QSR: z~ 6.4)• GRB 050904 X-ray flux
exceeded that of the brightest known X-ray QSO
SDSS J0130+0524,
by up to x105 , for days
← SDSS J0130 (multiplied by 100)
[ Watson et al 06 ApJ 637:L69 ]
Mészáros grb-gen06
• Prompt O/UV flash as bright as 990123 (~ 9th mag!) at same z (rev. shock..)• Eiso ~ 1054 erg, similarly very high ;decay similarly steep (~ t-3)• Observed at 800-1000 nm by TAROT (25 cm tel.!) [Boer et al, astro-ph/0510381]
TAROT (O/UV) ↑
Swift XRT ↓
Mészáros grb-gen06
• Need high Eiso ~ 1054 erg ? (or small beam?)• If reverse shock rest frame spectrum in UV
(relativistic reverse shock?) → ground detection @ O/IR: need high z (or else need enough rest-frame spectrum extending
redwards of Lyα, so not absorbed)• Need burst with strong flares (weak “smooth” afterglow
component)?• Other non-obs. or weak flash: pair formation, or weak
field in ejecta → rest-frame spectrum shifted to IR?
Why 050904 and 990123 ?
Mészáros grb-gen06
Origin of prompt Opt-flash• 4 prompt optical flashes have been measured while the
gamma-rays were still in progress• in some (GRB 050904, Boer et al, astro-ph/0510381; also
GRB 041219a, Vestrand et al, astroph/0503521) - prompt optical l.c. correlates with gamma-rays ⇒ emission from the same region? (e.g. internal shock? )
• in others (GRB 050401, Rykoff et al astroph/0508495, GRB 990123, Akerloff et al 00)
- prompt optical l.c. does NOT correlate with gamma-rays
⇒ emission from different region ? (e.g. reverse shock?)
56
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Different prompt gamma/opt correlations?
57Vestrand et al, 06, aph/0503521
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GRB 060218 / SN 2006aj
• Long(est) BAT T90 = 2100 s duration• XRT after 100 s, rising to max at ~1000s, followed by
steep decay, then PL decay• UVOT brightening to UV plateau @ 30ks
and later O plateau @ 40ks, decay to minimum @200ks, rebrightening @700ks
• XR non-thermal plus increasing BB component which dominates before the steep decay @1000s (kTBB ~ 0.17 keV)
58
Campana et al, Nature in press, astro-ph/0603279
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GRB 060218/ SN 2006aj
Interpreted as shock break-out of an anisotropic, semi-relativistic component from an optically thick progenitor stellar wind (Campana et al 06;
Note: Fan-Piran alternate model: their objections apply to spherical single component, whereas here assumed 2+ components, anisotropic semirelativistic + spher. envelope)
UVOT
BB comp. temp. & radius
Mészáros grb-gen06
Conclusions• Swift is significantly expanding our view & understanding of afterglows• New early XR, O features appear to be understandable within context
of standard afterglow model, with (not quite mastered) extensionsUnderstanding of new XR “smooth” features is reasonable, but fluiddynamics remains controversial - and MHD may play a large role.
• XR flares are significant challenge, also for progenitor, central engine • Relation of early XRT, UVOT to BAT flux levels pose challenges to
prompt GRB gamma-ray mechanisms (efficiencies, etc..)• Commonality & differences between short and long GRB afterglow
features will yield important clues, need much further work (diff. due to lower Eiso, broader θjet, E vs. Irr, Sp hosts?) • Information on long and short GRB jet breaks (collimation) not very
extensive yet, possibly due to higher avg. z and lower fluxes?• O/UV late afterglows largely support forward shock AG interpretation• Prompt O/IR flash detection may hold vital clues (rareness? reverse
shock interpretation? other..?)• Potential for high-z IGM probing, SFR mapping appears poised for
transition from wish to actual data to be modeled → cosmology.
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